Pipelines run subsea occasionally require repairs. In many installations, the pipeline is jacketed with a concentric jacket which leaves an annular space between the pipeline and the outside of the jacket. In the past, in order to service such pipelines using known subsea cutting devices, the entire pipeline had to be severed by a cutting apparatus. Generally, these devices would be lowered to the pipeline and use a frame-supported diamond wire as the cutting mechanism. The devices of the prior art oriented the diamond wire to make a cut perpendicular to the longitudinal axis of the pipeline, through the pipeline and the surrounding jacket. This step would be repeated at another location so that an entire segment, which is thought to have a leak, can be removed and replaced.
The devices previously known did not have the capability of cutting away the outer jacket without also cutting through the pipe. An advantage that is obtained from the present invention, which has the capability of independently cutting the outer jacket without cutting through the pipe, is that the pipeline can be exposed to confirm the precise location of any leak and to, perhaps, make any repairs without having to needlessly remove a complete section of the pipeline. The present invention is not limited to cuts in a single plane transverse to the longitudinal axis of the pipe. As a result, a multiplanar cut can reduce binding on the cutter since the cut piece remains in place at the end of the cut.
Typical of cutting devices available in the prior art are U.S. Pat. Nos. 5,685,996; 5,598,754; 5,361,748; 5,010,694; 4,777,723; 4,312,498; 4,143,862; 4,091,514; 3,578,233; 3,056,267; 2,762,621; U.S. Statutory Invention Registration H-45; European application 0540834A1; Russian patents 777146; 659,687; 150,377; and Japanese patent 2-59273. Yet other patents deal with cutting devices generally and components therefor, whether such devices are used subsea or to cut other structures. Typical of such devices are U.S. Pat. Nos. 4,936,284; 4,765,307; 4,007,705; 3,479,830; 2,795,222; 2,674,238; and 1,689,829. U.S. Pat. No. 4,109,480 shows an underwater crane that can be used for repair of pipelines underwater.
None of these prior art devices have the capability of selectively removing an outer jacket from a covered subsea pipeline, coupled with the versatility of being able to cut perpendicular to the longitudinal axis or in a multiplicity of planes if, for any reason, a section has to be severed from the pipeline for repair. One of the objects of the present invention is to provide a device which can be economical to build and which works efficiently to give flexibility to make a variety of different types of cuts to address any particular subsea situation. Another object of the device is to be able to remove a section of an outer jacket without cutting the actual pipeline to provide access to the pipeline for analysis of the location of a trouble spot and for possibly effecting a repair without cutting through the pipeline. These and other advantages of the apparatus of the present invention will become more apparent from a review of the detailed description below.